Bottom mount refrigerators include a freezer compartment on the bottom, with the fresh food or refrigerator compartment above the freezer compartment. One or more doors provide access to the fresh food compartment, and a separate door provides access to the freezer compartment. The freezer door or doors may be drawer-type doors that are pulled out, or they may be hingedly connected similar to the refrigerator compartment doors, such that they are rotated to provide access within.
The refrigerator and freezer compartments may be cooled using a single evaporator cooling system, in which the single evaporator cools air to be directed to the compartments to keep them at a predetermined temperature, or the refrigerator may include a dual evaporator system. Dual evaporator systems include two evaporators in the cooling cycle, with the separate evaporators dedicated to cooling air for a specific compartment (i.e., one evaporator for the refrigerator compartment, and one for the freezer compartment).
A cooled refrigerant is passed through the evaporator. The cold liquid-vapor mixture of refrigerant travels through the evaporator coil or tubes and is completely vaporized by cooling the warm air (from the space being refrigerated) being blown by a fan across the evaporator coil or tubes. However, because the refrigerant that passes through the coils of the evaporator is at a cold temperature, frost can form on the coils, especially when the cooling system is cooling a freezer compartment or other low temperature compartment. If too much frost forms on the coils, the evaporator will freeze up, and the cooling system will not properly cool the compartment(s) of the refrigerator.
Therefore, defrost systems are placed on or near the evaporators to aid in melting the frost off the coils, generally when the cooling system is not running (i.e., when the temperatures of the compartment(s) are at or below the set/predetermined temperatures). Most refrigerator evaporators use an electrical heater to defrost. The frost melts off the evaporator coils and drains to a pan in the machine compartment. The water in the pan evaporates into the air, which is routed to room air. The use of an electrical heater requires electricity to warm the heater, which can increase the cost of electricity required to run the refrigerator.
As the costs of energy increases, consumers have demanded low energy appliances to try to keep their bills at a minimum. Therefore, there is a need in the art for a low energy solution to defrost the evaporator coils in a refrigerator cooling system, which includes removing an electrical heater or warming component from the evaporator coils.